To Find :
The acceleration of the heavier object.
Solution :
Force of gravitation on lighter object by heavier object is :

Acceleration of lighter object is given by :
.....1)
Now, acceleration of heavier object when separation between them is 25 km :
.....2)
Putting value of m in equation 2, we get :

Therefore, the acceleration of the heavier object is 100 m/s².